Composition based on poly(arylene ether ketone) having improved properties

ABSTRACT

The present invention relates to a composition based on poly(ether ether ketone) (PEEK) comprising poly(ether ketone ketone) (PEKK), characterized in that the poly(ether ketone ketone) (PEKK) comprises a mixture of terephthalic and isophthalic units, the percentage by weight of terephthalic units, with respect to the sum of the terephthalic and isophthalic units, being between 55 and 85%, limits included, and preferably between 55 and 70%, the said composition comprising between 1 and 40%, limits included, preferably between 5 and 40% and more preferably still between 10 and 30% by weight of PEKK, with respect to the total weight of the composition.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to French Application No. 1460158,filed Oct. 22, 2014, the entire disclosure of which is incorporatedherein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The invention relates to the field of poly(arylene ether ketone)s andmore specifically to that of compositions based on poly(ether etherketone) (denoted PEEK in the continuation of the description).

More particularly, the invention relates to a composition based onpoly(ether ether ketone (PEEK) having improved properties and also to aprocess for improving at least one property of a PEEK-based composition.The composition according to the invention more particularly exhibits aslow rate of crystallization and, on the other hand, better mechanicalproperties.

DESCRIPTION OF THE RELATED ART

Poly(arylene ether ketone)s (PAEKs) are high performance materialshaving elevated thermomechanical properties. They are composed ofaromatic nuclei bonded via an oxygen atom (ether) and/or via a carbonylgroup (ketone). Their properties depend mainly on the ether/ketoneratio. In the preceding abbreviations, E denotes an ether functionalgroup and K denotes a ketone functional group. In the continuation ofthe document, these abbreviations will be used instead of the usualnames to denote the compounds to which they relate.

Poly(arylene ether ketone)s are used for applications restricting intemperature and/or mechanical stresses, indeed even chemical stresses.These polymers are encountered in fields as varied as aeronautics,offshore drilling operations or medical implants. They can be employedby moulding, extrusion, compression, spinning or also laser sintering.

In the family of PAEKs, the poly(ether ether ketone) (PEEK) isparticularly used in the context of the abovementioned applications.However, it exhibits the disadvantage of crystallizing very rapidly,which can generate large internal stresses in the manufactured partsbased on this material during the cooling thereof. In some cases, suchas PEEK coatings of metal parts or in the case of bulk PEEK parts, theseinternal stresses can result in splitting of the material. A subsequentannealing stage, followed by slow cooling, is generally necessary inorder to remove or at least reduce these internal stresses. In point offact, such a stage proves to be lengthy and thus involves a notinsignificant additional expenditure for the parts thus manufactured.

Furthermore, in the specific case of laser sintering, the rapid kineticsof crystallization can result in deformation of the part. Suchdeformation is also known as “curling”. Consequently, in this case, thegeometry of the part is not optimal.

Finally, even if the PEEKs already have good mechanical properties, itcan be advantageous, for some applications, to further improve themechanical properties of objects obtained by different types ofprocesses such as moulding, injection moulding, extrusion or lasersintering. Thus, it can be advantageous to increase the yield pointstress in order to be able to work a PEEK-based material under higherstresses without irreversibly deforming it but without, however, causinga deterioration in the other mechanical properties, such as elongationat break, for example. This is because an increase in the yield pointstress conventionally amounts to lowering the value of the elongation atbreak of a material. In point of fact, for some applications, it can beimportant to retain a ductile material with a high elongation at break.It is thus generally advisable to find a compromise between theelongation at break and the yield point, in order to have a plasticmaterial exhibiting mechanical properties suitable for the applicationfor which it is dedicated.

A polymer alloy comprising between 60 and 98% by weight of asemicrystalline PAEK and between 40 and 2% by weight of an amorphousPAEK is known from the document U.S. Pat. No. 5,342,664. Such an alloyexhibits a higher elongation at break and a reduced viscosity incomparison with the semicrystalline PAEK alone. However, this documentremains silent with regard to the rate of crystallization whichgenerates the problems of deformations of parts or requires a lengthyand expensive postannealing stage in order to eliminate the internalstresses which have appeared in the part as a result of excessivelyrapid crystallization kinetics. Neither is mention made of the yieldpoint of the alloy.

The paper entitled “Blends of two PAEK” which appeared in the reviewPOLYMER, 1988, Vol. 29, June, pp. 1017-1020, describes the preparationof an alloy based on PEEK and on PEK, two polymers of the family of thePAEKs which have the distinguishing feature of both crystallizingquickly. This paper studies the crystallization of the two compounds ofthe alloy and their behaviour. On the other hand, this document studiesneither the rate of crystallization and its influence on the appearanceof internal stresses and on the deformation of the parts obtained northe mechanical properties of the alloy.

The paper entitled “Dynamic study of crystallization and melting-inducedphase separation in PEEK/PEKK blends”, Journal of the American ChemicalSociety, 1997, 30, pp.4544-4550, describes an alloy of PEEK and PEKK,the T/I ratio of which of the terephthalic units (T) to the isophthalicunits (I) is 30/70. This document demonstrates that the incorporation of30/70 PEKK in PEEK, in proportions by weight equal to 50/50, makes itpossible to slow down the crystallization of the PEEK as a result of aninterdiffusion of the two compounds of the alloy. This document does notstudy the mechanical properties of such an alloy.

It is thus an aim of the invention to overcome at least one of thedisadvantages of the prior art. In particular, it is an aim of theinvention to provide a PEEK-based composition, at least one property ofwhich is improved, and a process for improving at least one property ofsuch a PEEK-based composition, so as to make possible the preparation ofparts from such a composition which exhibit a significant reduction inthe internal stresses so that it is possible to dispense with theadditional postannealing stage, which are not deformed and which exhibitenhanced mechanical properties.

BRIEF SUMMARY OF THE INVENTION

Surprisingly, it has been discovered that a composition based onpoly(ether ether ketone) (PEEK) comprising poly(ether ketone ketone)(PEKK), characterized in that the poly(ether ketone ketone) (PEKK)comprises a mixture of terephthalic and isophthalic units, thepercentage by weight of terephthalic units, with respect to the sum ofthe terephthalic and isophthalic units, being between 55 and 85%, limitsincluded, and preferably between 55 and 70%, the said compositioncomprising between 1 and 40%, limits included, preferably between 5 and40% and more preferably still between 10 and 30% by weight of PEKK, withrespect to the total weight of the composition, exhibits not onlyslowing in the kinetics of crystallization, in comparison with that of apure PEEK, but also a gain with regard to two, generally antagonistic,mechanical properties, since the yield point stress and the elongationat break are both increased, in comparison with a pure PEEK.

According to other optional characteristics of the composition:

-   -   the PEEK can be replaced with PEK or PEKEKK,    -   the PEKK can be a PEKK blend, each PEKK exhibiting a percentage        by weight of terephthalic units, with respect to the sum of the        terephthalic and isophthalic units, of between 55 and 85%,        limits included, and preferably between 55 and 70%,    -   the composition additionally comprises at least one filler        and/or at least one additive,    -   the proportion by weight of PEEK in the composition comprises        from 60 to 99%, limits included, preferably between 60 and 95%        and more preferably still between 70 and 90%, with respect to        the total weight of the composition.

Another subject-matter of the invention is a process for improving atleast one property of a PEEK-based composition, the said processconsisting in incorporating PEKK in the said PEEK-based composition, thesaid process being characterized in that the PEKK comprises a mixture ofterephthalic and isophthalic units, the percentage by weight ofterephthalic units, with respect to the sum of the terephthalic andisophthalic units, being between 55 and 85%, limits included, andpreferably between 55 and 70%, and in that the PEKK is incorporated inthe said composition in proportions of between 1 and 40%, limitsincluded, preferably between 5 and 40% and more preferably still between10 and 30% by weight, with respect to the total weight of thecomposition.

Finally, the invention relates to an object manufactured from acomposition as described above by a technology chosen from lasersintering, moulding, injection moulding or extrusion.

DESCRIPTION OF THE FIGURES

Other advantages and characteristics of the invention will becomeapparent on reading the following description, given as illustrative andnonlimiting example, with reference to the appended figures, whichrepresent:

FIG. 1, the change in the heat flow of seven PEEK-based compositions asa function of temperature,

FIG. 2, the change in the degree of crystallization of four PEEK-basedcompositions with respect to time.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

The composition which is a subject-matter of the invention is based onPEEK. The constituent PEEK matrix of the composition can also bereplaced by PEK or PEKEKK. In the abbreviations used, E denotes an etherfunctional group and K denotes a ketone functional group.

The presence of PEKK, possessing terephthalic and isophthalic units, inthe PEEK-based composition makes it possible to slow down the kineticsof crystallization of the PEEK, and thus to limit the internal stresseswhich may result in splits during the cooling of the material, and toobtain nondeformed parts, the geometry of which meets expectations.Terephthalic and isophthalic unit is understood to mean the formula ofterephthalic acid and isophthalic acid respectively.

Preferably, the PEKK incorporated in the PEEK-based compositioncomprises a percentage by weight of terephthalic units, with respect tothe sum of the terephthalic and isophthalic units, of between 55 and85%, limits included, more preferably still between 55 and 70% and morepreferably still of the order of 60%. Such a PEKK with approximately 60%of terephthalic units is a material having very slow crystallization,typically 20 minutes during an isothermal crystallization attemperatures of between 240 and 260° C., and exhibiting a glasstransition temperature Tg of the order of 160° C. and a melting point ofthe order of 305° C.

In particular, the variation in the proportions of terephthalic andisophthalic units of the PEKK, within the abovementioned range ofproportions, makes it possible to adjust the said kinetics ofcrystallization of the PEEK. The kinetics of crystallization will bestudied either under anisothermal conditions, that is to say during thecooling via a temperature gradient, or under isothermal conditions, thatis to say that the degree of crystallization will be monitored at agiven temperature. In the case of the study of the crystallization underanisothermal conditions, the lower the crystallization temperature, theslower the kinetics of crystallization. It is consequently possible toobtain a range of compositions based on PEEK and on PEKK, for which therate of crystallization is known for each composition and is adaptedaccording to the subsequent application of the said compositions.

Preferably, the composition comprises between 60 and 99%, limitsincluded, preferably between 60 and 95% and more preferably stillbetween 70 and 90% by weight of PEEK, with respect to the total weightof the composition, and between 1 and 40%, limits included, preferablybetween 5 and 40% and more preferably still between 10 and 30% by weightof PEKK, with respect to the total weight of the composition.

Such a composition advantageously makes it possible to improve two,generally antagonistic, mechanical properties of the PEEK. This isbecause the addition of PEKK possessing terephthalic and isophthalicunits, in the abovementioned proportions, with a percentage by weight ofbetween 1 and 40%, preferably between 5 and 40% and more preferablystill between 10 and 30%, with respect to the total weight of thecomposition, makes it possible to obtain a gain of between 5 and 15% inthe yield point and an elongation at break improved by a factor whichcan range up to 3.

The composition can in addition comprise one or more additives orcontain different compounds, such as fillers, in particular inorganicfillers, such as carbon black, nanotubes, short (glass or carbon)fibres, long fibres, ground or nonground fibres, stabilizing agents(light, in particular UV, and heat stabilizing agents), glidants, suchas silica, or also optical brighteners, dyes, pigments or a combinationof these fillers and/or additives.

The composition which has just been described consists of a PEEK-basedmatrix. In an alternative form, the PEEK matrix can be replaced with aPEK or PEKEKK matrix.

In addition, the PEKK incorporated in the PEEK-based composition, orPEK-based or PEKEKK-based composition, can be a PEKK blend, providedthat each PEKK exhibits a percentage by weight of terephthalic units,with respect to the sum of the terephthalic and isophthalic units, ofbetween 55 and 85%, preferably between 55 and 70% and more preferablystill of the order of 60%.

In addition, the invention relates to a process for improving at leastone property of a PEEK-based composition, the said process consisting inincorporating PEKK in the said PEEK-based composition. The incorporatedPEKK comprises a mixture of terephthalic and isophthalic units, thepercentage by weight of terephthalic units, with respect to the sum ofthe terephthalic and isophthalic units, being between 55 and 85% andpreferably between 55 and 70% and more preferably still of the order of60%. Advantageously, the PEKK is incorporated in the said composition inproportions of between 1 and 40%, preferably between 5 and 40% and morepreferably still between 10 and 30% by weight, with respect to the totalweight of the composition.

Such an incorporation of PEKK in the PEEK-based composition makes itpossible not only to adjust the kinetics of crystallization of the PEEKbut in addition to improve two mechanical properties of the PEEK whichare generally antagonistic, namely the yield point and the elongation atbreak.

The composition based on PEEK and on PEKK as defined above can beprepared by any known method which makes it possible to obtain ahomogeneous blend containing the composition according to the inventionand optionally other additives, fillers or other polymers. Such a methodcan be chosen from melt extrusion, compacting or also mixing techniques,for example using a roll mill.

More particularly, the composition according to the invention isprepared by melt blending all its components, in particular in a“direct” process.

In the case of laser sintering, the composition can also be obtained bya dry blending of powders.

Advantageously, the composition can be obtained in the form of granulesby compounding on a device known to a person skilled in the art, such asa twin-screw extruder, a cokneader or an internal mixer.

The composition thus prepared can subsequently be converted, for asubsequent conversion or use known to a person skilled in the art, usingdevices such as an injection moulding machine, an extruder, and thelike.

The process for the preparation of the composition according to theinvention can also use a twin-screw extruder feeding, withoutintermediate granulation, an injection moulding machine or an extruderaccording to a processing arrangement known to a person skilled in theart.

It is possible, starting from the composition obtained, which can beeither granules or powders, to manufacture different objects by a lasersintering or injection moulding or extrusion technique, for example.

The following examples illustrate, without implied limitation, the scopeof the invention:

EXAMPLE 1 Compounding of Several Compositions Exhibiting DifferentFormulations

The compounding is a process which makes it possible to blend, bymelting, plastics and/or additives and/or fillers.

In order to manufacture each composition, the starting materials, whichare provided in the form of granules, are placed in a corotatingtwin-screw extruder. The feed zone of the extruder is heated to atemperature of the order of 300° C.

The blending of the materials takes place under molten conditions at atemperature of the order of 360° C., with a rotational speed of 300revolutions/minute and a throughput of 2.5 kg/h.

The different compositions which were manufactured by compounding inorder to be compared all comprise PEEK and PEKK in different proportionsby wieght. The PEKK incorporated in the composition is a PEKK comprisingterephthalic (T) and isophthalic (I) units, the T/I ratio of which isequal to 60/40. Two different grades of PEKK were used. These two gradescomprise the same proportions of terephthalic units. They differ fromone another essentially in their viscosity. Thus, a first PEKK,referenced K1 in Table I and II below and sold by Arkema under thecommercial reference Kepstan® 6001, exhibits a viscosity number of 0.95dl/g, whereas the second PEKK, referenced K3 in the table I below andsold by Arkema under the commercial reference Kepstan® 6003, exhibits aviscosity number of 0.82 dl/g. The viscosity number is measuredaccording to Standard ISO 307, in solution at 25° C. in 96% sulphuricacid.

In these comparative examples, the proportion by weight of PEKK in thecomposition varies between 10 and 30% of the total weight of thecomposition for table I and from 5 to 50% for table II. The compositionsbased on PEEK and on PEKK are intended to be compared with a controlcomposition, referenced CC (table I), comprising solely pure PEEK, soldby Victrex under the commercial reference Victrex 450G, and referencedCT (table II), comprising solely pure PEEK, sold by Victrex under thecommercial reference Victrex 150G.

The different compositions produced are combined in Table I and IIbelow. The amounts of the different constituents of the composition,that is to say of PEEK and of PEKK, are expressed as percentage byweight, with respect to the total weight of the composition.

TABLE I CC C1 C2 C3 C4 C5 C6 PEEK 450G 100% 90% 80% 70% 90% 80% 70% PEKK(K1) 10% 20% 30% PEKK (K3) 10% 20% 30%

TABLE II CT C1a C2a C3a C4a C5a PEEK 150G 100% 95% 90% 80% 70% 50% PEKK(K1)  5% 10% 20% 30% 50%

EXAMPLE 2 Study of the Kinetics of Crystallization of the CompositionsObtained on Conclusion of the Compounding Process of Example 1

A crystallization study was carried out on the control sample of PEEK,referenced CC in Table I above, and on the six samples of compositionsreferenced C1 to C6 in Table I above.

The crystallization study is carried out by differential scanningcalorimetry, denoted DSC. DSC is a thermal analysis technique whichmakes it possible to measure the differences in the heat exchangesbetween a sample to be analyzed and a reference.

Use was made, in order to carry out this crystallization study, of the Q2000 device from TA Instruments. The study was carried out underanisothermal and isothermal crystallization conditions.

Anisothermal Crystallization

The protocol for DSC under anisothermal conditions, on the differentsamples CC and C1 to C6 resulting from Example 1, consists, in a firststep, in stabilizing the temperature at 20° C. The temperature issubsequently gradually increased, along a gradient of 20° C. per minute,up to 400° C. and then it is again gradually decreased down to 20° C.,along a reverse gradient of 20° C. per minute.

The crystallization is studied during the cooling stage. The heat flowis measured as a function of temperature and a curve representing thechange in the heat flow as a function of temperature is obtained foreach composition studied. These curves are represented in FIG. 1. Thecrystallization temperature, denoted Tc and expressed in degreesCelsius, is subsequently determined for each composition by projectingthe maximum of the corresponding curve onto the axis of the abscissae.This determination is carried out directly by the DSC equipment used.

The crystallization temperatures Tc of each sample analyzed are combinedin Table II below.

TABLE II Composition Tc (° C.) CC 291.3 C1 289.1 C2 288.0 C3 286.6 C4289.1 C5 287.7 C6 286.7

The curve of the control composition CC (pure PEEK), which does notcomprise PEKK, is the curve located furthest to the right in the graphof FIG. 1. This control composition exhibits a crystallizationtemperature Tc_(cc) which is the highest, equal to 291.3° C.

These curves demonstrate that, the higher the fraction by weight of PEKKin the composition, the lower the crystallization temperature and thusthe more the crystallization is delayed. The addition of PEKK to thePEEK according to the invention thus makes it possible to delay thecrystallization of the PEEK.

Isothermal crystallization

DSC under isothermal conditions was carried out for a sample of controlcomposition CC and samples of the compositions C1, C2 and C3respectively comprising 10%, 20% and 30% by weight of PEKK. The protocolof the isothermal DSC comprises the following three stages: a firststage consists, in a first step, in stabilizing the temperature at 20°C., a second stage subsequently consists in gradually increasing thetemperature, along a gradient of 20° C. per minute, up to 400° C.Finally, the temperature is reduced from 400° C. down to 315° C., alonga gradient of 20° C. per minute, and then it is stabilized at 315° C.for one hour.

During the hour of stabilization of the temperature at 315° C., thefraction by weight of PEEK crystallized as a function of time t ismeasured. The measurements are carried out on the compositions C1, C2and C3, in comparison with the control composition CC. The four curvesobtained are represented in the graph of FIG. 2.

It results from the curve corresponding to the control sample CC thatthe crystallization half time is approximately 6 minutes. Thecrystallization half time of a polymer is the time necessary for thecrystallization of 50% of this polymer. On the curves of FIG. 2, it isdetermined by being placed at the value of 50% on the axis of theordinates (% of crystallized PEEK) and by projecting this value onto theaxis of the abscissae (Time).

The curve corresponding to the composition C3 is offset to the right byapproximately 4 minutes, with respect to the curve of the controlcomposition CC. The crystallization half time on this curve isapproximately 10 minutes. The curves corresponding to the compositionsC1 and C2 are offset to the right by approximately 3 minutes, withrespect to the curve of the control composition CC, the crystallizationhalf time of the composition C1 being approximately 9 minutes and thatof the composition C2 being virtually 10 minutes.

It results from these curves that, surprisingly, the delay incrystallization is not proportional to the content of PEKK incorporatedin the composition. Contrary to what might have been expected, thechange in crystallization kinetics is not linear as a function of thecontent of PEKK incorporated. Consequently, it is preferable toincorporate a content of PEKK of less than or equal to 40% by weight,with respect to the total weight of the composition, in order to preventthe appearance of a phenomenon of phase separation in the composition.

The addition of PEKK in a proportion of 1 to 40% by weight, preferablybetween 5 and 40% by weight and more preferably still between 10 and 30%by weight, with respect to the total weight of the PEEK-basedcomposition according to the invention, thus makes it possible to delaythe crystallization of the PEEK, while avoiding a phenomenon of phaseseparation.

EXAMPLE 3 Measurement of the Yield Point Stress and of the Elongation atBreak of Injection-Moulded Parts Based on the Compositions Obtained onConclusion of the Compounding Process of Example 1

In order to be able to carry out measurements of yield point stress andof elongation at break, test specimens of samples were produced in afirst step. For this, an injection moulding machine is used. In thisexample, the injection moulding machine used is a Battenfeld 80Tmoulding machine. The feed temperature of the moulding machine isregulated at 350° C., the temperature of the injection nozzle isregulated at 390° C. and the temperature of the mould is set at 230° C.

Test specimens appropriate for tensile tests of 1BA type according toStandard ISO 527 are then obtained.

For the comparative tests of measurement of yield point stress and ofelongation at break, two test specimens were produced according toStandard ISO 527 1BA. A first test specimen of the control compositionCC is compared with a second test specimen of the composition C3 ofExample 1, comprising 30% by weight of PEKK, and the same procedure wasrepeated for controle composition CT compared with specimen C10 to C5a.

The measurements of stress were carried out on each test specimen usinga tensile testing device coupled to an optical extensometer, makingpossible the recording of the curves of stress as a function of thestrain of the test specimens subjected to a tensile stress. The tensiletesting device used for these tests is more particularly a tensiletesting device from Zwick sold under the reference Zwick 1455.

The measurements are carried out at 23° C., at a relative humidity of50% RH and at a pull rate of 25 mm/min.

The tensile force necessary as a function of the elongation is thenmeasured and the yield point stress and the elongation at break aredetermined. The results obtained are combined in Table III and IV below.

TABLE III Yield point Elongation at Composition stress (MPa) break (%)CC 92.5 40 C3 101 100

TABLE IV Yield point Elongation at Composition stress (MPa) break (%) CT103 70 C1a 103 85 C2a 103 100 C3a 102 110 C4a 102 85 C5a 99 50

The addition of 30% by weight of PEKK to PEEK makes it possible tochange the yield point stress from 92.5 MPa to 101 MPa, i.e. an increaseof 7.5% in results from table III. Furthermore, this addition makes itpossible to increase the elongation at break from 40% to 100%, i.e. anincrease by a factor of 2.5.

From Table IV, same conclusion can be formulated for elongation atbreak. Additionally, 50% composition (C5a) which is out of the claimedcompositions shows that maximum of PEKK to be advantageously mixed withPEEK should be 40%, not more.

Thus, the incorporation of PEKK in a PEEK-based composition brings aboutan increase in the yield point stress and also an increase in theelongation at break and thus an increase in two mechanical propertieswhich are generally antagonistic.

The composition according to the invention exhibits not only theadvantage of slowing down the kinetics of crystallization of PEEK, andthereby of reducing the internal stresses of the material, of thusdispensing with a lengthy and expensive post annealing stage and ofobtaining non deformed parts having the desired optimum geometry, but itexhibits in addition the advantage of having exceptional mechanicalproperties with a gain in the yield point and in the elongation atbreak, which were until now known to be antagonistic mechanicalproperties.

What is claimed is:
 1. A composition comprising a) a polymer selectedfrom poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK) orpoly(ether ketone ether ketone ketone) (PEKEKK) and b) poly(ether ketoneketone) (PEKK), wherein the poly(ether ketone ketone) (PEKK) comprises amixture of terephthalic and isophthalic units, the percentage by weightof terephthalic units, with respect to the sum of the terephthalic andisophthalic units, being between 55 and 85%, limits included, andwherein the composition is comprised of between 1 and 40%, limitsincluded, by weight of PEKK, with respect to the total weight of thecomposition.
 2. The composition according to claim 1, wherein the PEKKis a PEKK blend, each PEKK exhibiting a percentage by weight ofterephthalic units, with respect to the sum of the terephthalic andisophthalic units, of between 55 and 85%, limits included.
 3. Thecomposition according to claim 1, wherein the composition comprises atleast one filler and/or at least one additive.
 4. The compositionaccording to claim 1, wherein the composition is comprised of PEEK andthe proportion by weight of PEEK in the composition is between 60 and99%, limits included, with respect to the total weight of thecomposition.
 5. The composition according to claim 1, wherein thepercentage by weight of terephthalic units, with respect to the sum ofthe terephthalic and isophthalic units, is between 55 and 70%.
 6. Thecomposition according to claim 1, wherein the composition is comprisedof between 5 and 40%, limits included, by weight of PEKK, with respectto the total weight of the composition.
 7. The composition according toclaim 1, wherein the composition is comprised of between 10 and 30%,limits included, by weight of PEKK, with respect to the total weight ofthe composition.
 8. The composition according to claim 1, wherein thePEKK is a PEKK blend, each PEKK exhibiting a percentage by weight ofterephthalic units, with respect to the sum of the terephthalic andisophthalic units, of between 55 and 70%, limits included.
 9. Thecomposition according to claim 1, wherein the composition is comprisedof PEEK and the proportion by weight of PEEK in the composition isbetween 60 and 95%, limits included, with respect to the total weight ofthe composition.
 10. The composition according to claim 1, wherein thecomposition is comprised of PEEK and the proportion by weight of PEEK inthe composition is between 70 and 90%, limits included, with respect tothe total weight of the composition.
 11. A process for improving theyield point and/or the elongation at break of a composition comprised ofpoly(ether ether ketone) (PEEK), poly(ether ketone) (PEK) or poly(etherketone ether ketone ketone) (PEKEKK), wherein the process comprisesincorporating PEKK in the composition, wherein the PEKK comprises amixture of terephthalic and isophthalic units, the percentage by weightof terephthalic units, with respect to the sum of the terephthalic andisophthalic units, being between 55 and 85%, limits included, andwherein the PEKK is incorporated in the composition in a proportion ofbetween 1 and 40%, limits included, by weight, with respect to the totalweight of the composition.
 12. The process according to claim 11,wherein the percentage by weight of terephthalic units, with respect tothe sum of the terephthalic and isophthalic units, is between 55 and70%, limits included.
 13. The process according to claim 11, wherein thePEKK is incorporated into the composition in a proportion of between 5and 40%, limits included, by weight, with respect to the total weight ofthe composition.
 14. The process according to claim 11, wherein the PEKKis incorporated into the composition in a proportion of between 10 and30%, limits included, by weight, with respect to the total weight of thecomposition.
 15. An object manufactured from a composition according toclaim 1 using a technology selected from the group consisting of lasersintering, moulding, injection moulding and extrusion.